Flatliners (R)
Inspired by the experiences of those who have ''died'' and returned to life, Nelson (Kiefer Sutherland), a sort of Brat Pack Dr. Frankenstein, leads his fellow medical students in a reckless experiment that involves shutting down heart, lungs, and brain for minutes at a time. Plunging into the afterlife, the characters come face to face with their sins! Once again director Joel Schumacher (''The Lost Boys'') works in a style that might be described as high rock video. You may go into ''Flatliners'' hoping for vicarious altered states, but the film -- a New Wave teen morality play -- is about as exciting as staring at a lava lamp or two hours. D

Problem Child (PG)
In this adopted-brat-from-hell comedy, the vicious little tyke's tricks are too unimaginative to be much fun -- though with jokes this lame, you won't have to worry much about your children getting any bad ideas. D-

Young Guns II (PG-13)
This sequel to 1988's plastic six-shooter marathon was directed by the talented New Zealander Geoff Murphy. Damned if he hasn't taken his teen-dream cast, his how-to-sell-out-quickly blockbuster-sequel assignment, and tried to come up with a real movie! He doesn't succeed (in today's Westerns, cliches remain cliches, even when they're well-crafted), yet the film is an honorable try. Emilio Estevez gives a giggly, one-note performance as Billy the Kid, who tries to escape a government posse by journeying toward the Mexican border along with the rest of the Regulator gang. The trouble with so many of today's young actors is that there's no deep-seated yearning or fury to their performances. They just seem like well-adjusted California kids putting on a show. C